A. Field of the Invention
This invention relates in general to an automatic temperature control system for automobiles, improved components thereof and the arrangement of such components within the system.
B. Description of the Prior Art
Automatic temperature control systems were first introduced in about 1964 in the United States and are now available on most large size cars. In the systems heretofore, the components of the system have been scattered throughout the car, being interconnected by vacuum and wiring harnesses. One of these systems, for instance, has a main component grouping on the power servo, with other hardware located on the dash control, in ducts, on the air conditioning case, and in the engine compartment. Another has many components grouped on the heater-air conditioning case, with other components on the dash control, under the dash and in the engine compartment. These systems are generally complicated, difficult to install and maintain, expensive to produce and inaccurate.
The components of such systems and their function is as set forth below:
1. Sensors--to sample in-car and ambient temperature;
2. Transducers--to convert the sensors' output to a control signal;
3. A power servo--to convert the control signal to a stroke, thereby driving program switches and a temperature door. Bimetal sensors have been used to sense temperature changes and provide a signal responsive thereto for many years. However, the signal from such a sensor is very small and is rarely able by itself to provide the necessary force to activate a mechanical or electrical system of which the sensor is a part;
4. Program switches--to control system functions such as air discharge location, blower speed, recirculation, water valve, on-off function, etc.;
5. A temperature blend door--to modulate the air discharge temperature from the heater-air conditioning system;
6. Dash controls--contains levers used by the driver of a car to adjust and set the system to the desired mode and condition of operation;
7. Selector switches13 operated by the dash controls;
8. Cold engine lockout (CELO) valve--to delay the system operation in its heater mode until the heater core is warm;
9. Compressor ambient switch--to control the compressor operation as a function of the ambient temperature;
10. A water valve--controlled by a program switch to turn water off to the heater core under maximum cooling conditions; and
11. A resistor block--contains a dropping resistor for fan speed control. This works in conjunction with the program switches.
There are many problems associated with these systems.
In operation, these systems generally have two sensors which individually sense the ambient and in-car temperature and convert these readings to either electronic or mechanical signals. The ambient signal is used to bias the in-car signal and the single output is used to control the operation of the system. The appropriate temperature is generally supplied by the operation of the temperature blend door whose opening and closing regulates the heat and air conditioning supplied from the heater and air conditioner.
Since the sensors are often mounted at the end of long tubes supplying the in-car and ambient air, error in the sensing apparatus is often introduced by the air passing through long super-heated stretches which bias the temperature of the incoming air. For instance, the in-car air is often sampled by letting air enter a tube which is underneath the dash. By the time the air reaches its sensor near the fire wall, the temperature of the air in the tube has often reached an elevated temperature to that of the original air by reason of bias occurring when the air passed through heated areas under the dash. This problem has sometimes been corrected by placing both sensors at the spot where sampling air was taken in, but this requires long electrical leads and electrical conversion signals for changing the temperature of the air sensed to an appropriate electrical value.
In these systems, the output stroke of the power servo is proportional to the vacuum level therein which in turn is proportional to the sensor signals from the two sampling devices. This is called a "proportional vacuum" system. A proportional vacuum system is subject to stroke hysteresis, i.e., there may be two different output strokes at the same vacuum level. As the transducer signal does not have a feedback loop, the sensors and transducers combination does not know where the servo motor stroke is at any given time, which causes drift, cycling and over-shoot.
Hysteresis is caused by the frictional forces required to drive the program switches, to open the temperature doors, by the override springs, and by various pin hole tolerances. Further, hysteresis is not constant from one system to another and will deteriorate with time.
In these prior art systems, as the vacuum level increases, the servo motor strokes towards maximum air conditioning mode operation while with decreasing vacuum the servo motor drives towards maximum heater conditon. The friction in the system, however, causes the stroke to reach different positions for the same temperature, depending on whether the vacuum is increasing or decreasing. Current systems take two steps to alleviate these conditons and effect acceptable control. One is to provide high vacuum levels so that the slope of the control curve increases. This serves to decrease the differences in stroke for the same temperature. The second means used is to provide low friction program switches. These two means do serve to reduce hysteresis, but they present problems themselves in that the use of high vacuum level is hard to attain on the present-day automobiles with their numerous pollution control devices, especially on long hill climbs and the use of low friction switches is expensive.
There are two types of vacuum motors, or power servos, currently used to supply output to a shaft from a supply of vacuum. These are often used to operate car doors, as well as to drive switches in an automatic temperature control system. Generally, these motors consist of two case halves (the cylinder) which entrap a diaphragm upon which is mounted a rigid piston with an output shaft. One case half has a port connected to a source of vacuum and the other half is open. As vacuum is varied through the port, the motor strokes towards and away from the case half containing the port.
One type of such motor in use now is called a rolling diaphragm motor. Here as the piston strokes towards the case half containing the port when vacuum is increased, the diaphragm transfers from the piston area to the cylinder. This provides maximum effective area for the cylinder diameter and allows the motor to take large pressure differences. However, the piston must always support the diaphragm requiring very deep case halves and the pressure differential cannot be reversed.
A second type of such motor or servo in present use is the flip-flop diaphragm motor. Here the diaphragm does not transfer from the piston to the case and has no defined convolute. This motor has the advantage of having a shallower case than does the rolling diaphragm motor and the motor can take pressure reversal. However, it requires a larger diameter for the same effective area achieved in a rolling diaphragm motor and it cannot take as much pressure differential as the rolling diaphragm motor can.
Vacuum switches or valves are used in automotive applications in an on-off mode to apply vacuum to various places within the system to open and shut air supply doors, etc. In the automatic temperature control system of the present invention, vacuum switches are used for such things as determining the air discharge location, blower speed, recirculation operation mode, water valve operation, etc. Several types of such switches are presently on the market, all of which have certain disadvantages.
One type is generally made of two die case pieces which are lapped smooth. Ports are provided in one half while the other has channels so that when the second half is rotated it either provides a channel from one port to the other so that vacuum can be switched from one port to another, or it closes the ports. These switches have generally required a fairly high force to overcome friction and cross-venting of the ports has resulted in serious vacuum leakage and loss of vacuum, especially on long hill climbs. This loss of vacuum causes a loss of control in all of the vacuum systems.
Another such switch has the movable portion made of rubber, which is molded to a metal plate. Here the switch has very small ports, on the order of 0.020 inches, with relatively large rubber sealing contact areas. The small size of the ports often allows blockage due to frost or accummulation of dirt.
A type of valve used to produce porportional vacuum is what is known as a dog bone valve. This has three modes of operation as follows:
(1) At rest, the dog bone component seals off both the vacuum and vent ports so that there is no operation of the overall valve;
(2) A diaphragm in the dog bone valve allows a vent body which surrounds the dog bone components to move in response to outside forces. When the valve is to supply additional vacuum, the valve body pulls upon the dog bone component and releases it from its seat, thereby allowing the vacuum level of the valve to increase to the supply level unless the dog bone component is first returned to its rest position; and
(3) When vacuum is to be decreased, the vent body is moved further into the valve until it is released from contact with the dog bone component, thus allowing venting of the vacuum within the valve. This venting continues until the vent body returns to its rest position in contact with the dog bone component.